;; Meant to be run on a REPL, this small script will find all the namespaces that are not transitively required
;; by a parent ns. This may be useful if you need to extract a small application from a huge monolithic project.

;; This code has been adapted from https://github.com/hilverd/lein-ns-dep-graph and distributed under the same license.

;; Note that this only looks at the ns declarations, but has no way to detect dependencies that are dynamically built
;; (e.g. by requiring a symbol created from a string using a plain `require`).

(do
  (import [java.io PushbackReader])
  (require '[clojure.java.io :as io])
  (require '[clojure.set :as set])
  (require '[clojure.edn :as edn])
  (require '[clojure.tools.namespace.file :as ns-file])
  (require '[clojure.tools.namespace.track :as ns-track])
  (require '[clojure.tools.namespace.find :as ns-find])
  (require '[clojure.tools.namespace.dependency :as ns-dep]))

(defn transitive-deps-of [source-paths, ns-parents]
  (let [source-files (apply set/union
                            (map #(ns-find/find-sources-in-dir %)
                                 (file-seq source-paths)))
        tracker (ns-file/add-files {} source-files)
        dep-graph (tracker ::ns-track/deps)
        ns-names (set (map (comp second ns-file/read-file-ns-decl)
                           source-files))
        part-of-project? (partial contains? ns-names)
        part-of-parents?  #(or (empty? ns-parents)
                               (contains? ns-parents %)
                               (boolean (seq (set/intersection ns-parents (ns-dep/transitive-dependents dep-graph %)))))
        nodes (->> (ns-dep/nodes dep-graph)
                   (filter part-of-project?)
                   (filter part-of-parents?))]
    nodes))


(let [source-paths (io/file "/path/to/my/project/src/main/clojure/")]
  (set/difference
   (set (transitive-deps-of source-paths #{'my.parent.ns}))
   (set (transitive-deps-of source-paths #{}))))